Norway rats aren’t small critters. Typically, they’re seven to nine inches in length with a six to eight-inch-long tail and are covered with coarse, shaggy brown hair. They may have small, flat noses, but they can smell sources of food from afar and have an excellent sense of taste.

They can be tough to catch as they tend to be more active at night, but there are a few sure signs of pests roaming around your property.

1. Gnaw marks

Nearly anything is fair game. From personal belongings to electrical wiring to furniture, Norway rats will leave gnaw marks behind. Even the structure of buildings is appetizing to Norway rats, which usually leave gnaw marks about two inches or more in diameter with rough edges.

4. Burrows

In order to make nests, Norway rats may burrow in areas next to walls, under buildings, beneath debris, and in a variety of spaces. Yet the pests also need a steady access to food and water and tend to live in close association with humans.

5. Grease marks

The oil and dirt that builds up on Norway rats will often be left behind in their tracks or on walls. That spot on your floor might not be from your muddy shoes after all — it could be grease marks. It’s time to look further into your foundation to get rid of the pesky creatures.